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<h1><span class="logo-braces">{ }</span> <a href="http://codemirror.net/">CodeMirror</a></h1>

<pre class="grey">
<img src="css/baboon.png" class="logo" alt="logo"/>/* User manual and
   reference guide */
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<div class="clear"><div class="leftbig blk">

    <h2 id="overview">Overview</h2>

    <p>CodeMirror is a code-editor component that can be embedded in
    Web pages. It provides <em>only</em> the editor component, no
    accompanying buttons, auto-completion, or other IDE functionality.
    It does provide a rich API on top of which such functionality can
    be straightforwardly implemented.</p>

    <p>CodeMirror works with language-specific modes. Modes are
    JavaScript programs that help color (and optionally indent) text
    written in a given language. The distribution comes with a few
    modes (see the <code>mode/</code> directory), and it isn't hard
    to <a href="#modeapi">write new ones</a> for other languages.</p>

    <h2 id="usage">Basic Usage</h2>

    <p>The easiest way to use CodeMirror is to simply load the script
    and style sheet found under <code>lib/</code> in the distribution,
    plus the script and style sheet for the mode(s) you want to use.
    (See also <a href="compress.html">the compresion helper</a>.) For
    example:</p>

    <pre>&lt;script src="lib/codemirror.js">&lt;/script>
&lt;link rel="stylesheet" href="lib/codemirror.css">
&lt;script src="mode/javascript/javascript.js">&lt;/script>
&lt;link rel="stylesheet" href="mode/javascript/javascript.css"></pre>

    <p>Having done this, an editor instance can be created like
    this:</p>

    <pre>var myCodeMirror = CodeMirror(document.body);</pre>

    <p>The editor will be appended to the document body, will start
    empty, and will use the mode that we loaded. To have more control
    over the new editor, a configuration object can be passed
    to <code>CodeMirror</code> as a second argument:</p>

    <pre>var myCodeMirror = CodeMirror(document.body, {
  value: "function myScript(){return 100;}\n",
  mode:  "javascript"
});</pre>

    <p>This will initialize the editor with a piece of code already in
    it, and explicitly tell it to use the JavaScript mode (which is
    useful when multiple modes are loaded).
    See <a href="#config">below</a> for a full discussion of the
    configuration options that CodeMirror accepts.</p>

    <p>In cases where you don't want to append the editor to an
    element, and need more control over the way it is inserted, the
    first argument to the <code>CodeMirror</code> function can also
    be a function that, when given a DOM element, inserts it into the
    document somewhere. This could be used to, for example, replace a
    textarea with a real editor:</p>

    <pre>var myCodeMirror = CodeMirror(function(elt) {
  myTextArea.parentNode.replaceChild(myTextArea, elt);
}, {value: myTextArea.value});</pre>

    <p>However, for this use case, which is a common way to use
    CodeMirror, the library provides a much more powerful
    shortcut:</p>

    <pre>var myCodeMirror = CodeMirror.fromTextArea(myTextArea);</pre>

    <p>This will, among other things, ensure that the textarea's value
    is updated when the form (if it is part of a form) is submitted.
    See the <a href="#fromTextArea">API reference</a> for a full
    description of this method.</p>

    <h2 id="config">Configuration</h2>

    <p>Both the <code>CodeMirror</code> function and
    its <code>fromTextArea</code> method take as second (optional)
    argument an object containing configuration options. Any option
    not supplied like this will be taken
    from <code>CodeMirror.defaults</code>, an object containing the
    default options. You can update this object to change the defaults
    on your page.</p>

    <p>Options are not checked in any way, so setting bogus options is
    bound to lead to odd errors.</p>

    <p>These are the supported options:</p>

    <dl>
      <dt id="option_value"><code>value (string)</code></dt>
      <dd>The starting value of the editor.</dd>

      <dt id="option_mode"><code>mode (string or object)</code></dt>
      <dd>The mode to use. When not given, this will default to the
      first mode that was loaded. It may be a string, which either
      simply names the mode or is
      a <a href="http://en.wikipedia.org/wiki/MIME">MIME</a> type
      associated with the mode. Alternatively, it may be an object
      containing configuration options for the mode, with
      a <code>name</code> property that names the mode (for
      example <code>{name: "javascript", json: true}</code>). The demo
      pages for each mode contain information about what configuration
      parameters the mode supports. You can ask CodeMirror which modes
      and MIME types are loaded with
      the <code>CodeMirror.listModes</code>
      and <code>CodeMirror.listMIMEs</code> functions.</dd>

      <dt id="option_indentUnit"><code>indentUnit (integer)</code></dt>
      <dd>How many spaces a block (whatever that means in the edited
      language) should be indented. The default is 2.</dd>

      <dt id="option_indentWithTabs"><code>indentWithTabs (boolean)</code></dt>
      <dd>Whether, when indenting, the first N*8 spaces should be
      replaced by N tabs. Default is false.</dd>

      <dt id="option_tabMode"><code>tabMode (string)</code></dt>
      <dd>Determines what happens when the user presses the tab key.
      Must be one of the following:
        <dl>
          <dt><code>"classic" (the default)</code></dt>
          <dd>When nothing is selected, insert a tab. Otherwise,
          behave like the <code>"shift"</code> mode. (When shift is
          held, this behaves like the <code>"indent"</code> mode.)</dd>
          <dt><code>"shift"</code></dt>
          <dd>Indent all selected lines by
          one <a href="#option_indentUnit"><code>indentUnit</code></a>.
          If shift was held while pressing tab, un-indent all selected
          lines one unit.</dd>
          <dt><code>"indent"</code></dt>
          <dd>Indent the line the 'correctly', based on its syntactic
          context. Only works if the
          mode <a href="#indent">supports</a> it.</dd>
          <dt><code>"default"</code></dt>
          <dd>Do not capture tab presses, let the browser apply its
          default behaviour (which usually means it skips to the next
          control).</dd>
        </dl></dd>

      <dt id="option_enterMode"><code>enterMode (string)</code></dt>
      <dd>Determines whether and how new lines are indented when the
      enter key is pressed. The following modes are supported:
        <dl>
          <dt><code>"indent" (the default)</code></dt>
          <dd>Use the mode's indentation rules to give the new line
          the correct indentation.</dd>
          <dt><code>"keep"</code></dt>
          <dd>Indent the line the same as the previous line.</dd>
          <dt><code>"flat"</code></dt>
          <dd>Do not indent the new line.</dd>
        </dl></dd>

      <dt id="option_electricChars"><code>electricChars (boolean)</code></dt>
      <dd>Configures whether the editor should re-indent the current
      line when a character is typed that might change its proper
      indentation (only works if the mode supports indentation).
      Default is true.</dd>

      <dt id="option_lineNumbers"><code>lineNumbers (boolean)</code></dt>
      <dd>Whether to show line numbers to the left of the editor.</dd>

      <dt id="option_firstLineNumber"><code>firstLineNumber (integer)</code></dt>
      <dd>At which number to start counting lines. Default is 1.</dd>

      <dt id="option_gutter"><code>gutter (boolean)</code></dt>
      <dd>Can be used to force a 'gutter' (empty space on the left of
      the editor) to be shown even when no line numbers are active.
      This is useful for setting <a href="#setMarker">markers</a>.</dd>

      <dt id="option_readOnly"><code>readOnly (boolean)</code></dt>
      <dd>This disables editing of the editor content by the user.
      (Changes through API functions will still be possible.)</dd>

      <dt id="option_onChange"><code>onChange (function)</code></dt>
      <dd>When given, this function will be called every time the
      content of the editor is changed. It will be given the editor
      instance as only argument.</dd>

      <dt id="option_onCursorActivity"><code>onCursorActivity (function)</code></dt>
      <dd>Like <code>onChange</code>, but will also be called when the
      cursor moves without any changes being made.</dd>

      <dt id="option_onGutterClick"><code>onGutterClick (function)</code></dt>
      <dd>When given, will be called whenever the editor gutter (the
      line-number area) is clicked. Will be given the editor instance
      as first argument, and the (zero-based) number of the line that
      was clicked as second argument.</dd>

      <dt id="option_onFocus"><code>onFocus, onBlur (function)</code></dt>
      <dd>The given functions will be called whenever the editor is
      focused or unfocused.</dd>

      <dt id="option_onScroll"><code>onScroll (function)</code></dt>
      <dd>When given, will be called whenever the editor is
      scrolled.</dd>

      <dt id="option_matchBrackets"><code>matchBrackets (boolean)</code></dt>
      <dd>Determines whether brackets are matched whenever the cursor
      is moved next to a bracket.</dd>

      <dt id="option_workTime"><code>workTime, workDelay (number)</code></dt>
      <dd>Highlighting is done by a pseudo background-thread that will
      work for <code>workTime</code> milliseconds, and then use
      timeout to sleep for <code>workDelay</code> milliseconds. The
      defaults are 200 and 300, you can change these options to make
      the highlighting more or less aggressive.</dd>

      <dt id="option_undoDepth"><code>undoDepth (integer)</code></dt>
      <dd>The maximum number of undo levels that the editor stores.
      Defaults to 40.</dd>

      <dt id="option_tabindex"><code>tabindex (integer)</code></dt>
      <dd>The <a href="http://www.w3.org/TR/html401/interact/forms.html#adef-tabindex">tab
      index</a> to assign to the editor. If not given, no tab index
      will be assigned.</dd>

      <dt id="option_onKeyEvent"><code>onKeyEvent (function)</code></dt>
      <dd>This provides a rather low-level hook into CodeMirror's key
      handling. If provided, this function will be called on
      every <code>keydown</code> and <code>keypress</code> event that
      CodeMirror captures. It will be passed two arguments, the editor
      instance and the key event. This key event is pretty much the
      raw key event, except that a <code>stop()</code> method is
      always added to it. You could feed it to, for
      example, <code>jQuery.Event</code> to further normalize
      it.<br>This function can inspect the key event, and handle it if
      it wants to. It may return true to tell CodeMirror to ignore the
      event. Be wary that, on some browsers, stopping
      a <code>keydown</code> does not stop the <code>keypress</code>
      from firing, whereas on others it does. If you respond to an
      event, you should probably inspect its <code>type</code>
      property and only do something when it is <code>keydown</code>
      (or <code>keypress</code> for actions that need character
      data).</dd>
    </dl>

    <h2 id="styling">Customized Styling</h2>

    <p>Up to a certain extent, CodeMirror's look can be changed by
    modifying style sheet files. The style sheets supplied by modes
    simply provide the colors for that mode, and can be adapted in a
    very straightforward way. To style the editor itself, it is
    possible to alter or override the styles defined
    in <a href="lib/codemirror.css"><code>codemirror.css</code></a>.</p>

    <p>Some care must be taken there, since a lot of the rules in this
    file are necessary to have CodeMirror function properly. Adjusting
    colors should be safe, of course, and with some care a lot of
    other things can be changed as well. The CSS classes defined in
    this file serve the following roles:</p>

    <dl>
      <dt id="class_CodeMirror"><code>CodeMirror</code></dt>
      <dd>The outer element of the editor. This determines whether the
      editor scrolls (<code>overflow: auto</code> + fixed height). Can
      also be used to set styles that should hold for everything
      inside the editor, or to set a background.</dd>

      <dt id="class_CodeMirror_focused"><code>CodeMirror-focused</code></dt>
      <dd>Whenever the editor is focused, the top element gets this
      class. This is used to hide the cursor and give the selection a
      different color when the editor is not focused.</dd>

      <dt id="class_CodeMirror_gutter"><code>CodeMirror-gutter</code></dt>
      <dd>Use this for giving a background or a border to the editor
      gutter. Don't set any padding here,
      use <code>CodeMirror-gutter-text</code> for that. By default,
      the gutter is 'fluid', meaning it will adjust its width to the
      maximum line number or line marker width. You can also set a
      fixed width if you want.</dd>

      <dt id="class_CodeMirror_gutter_text"><code>CodeMirror-gutter-text</code></dt>
      <dd>Used to style the actual line numbers. For the numbers to
      line up, you'll want this style to use exactly the same font and
      vertical padding as normal edited text, as per
      the <code>CodeMirror-lines</code> class.</dd>

      <dt id="class_CodeMirror_lines"><code>CodeMirror-lines</code></dt>
      <dd>The visible lines. If this has vertical
      padding, <code>CodeMirror-gutter</code> should have the same
      padding.</dd>

      <dt id="class_CodeMirror_cursor"><code>CodeMirror-cursor</code></dt>
      <dd>The cursor is a block element that is absolutely positioned.
      You can make it look whichever way you want.</dd>

      <dt id="class_CodeMirror_selected"><code>CodeMirror-selected</code></dt>
      <dd>The selection is represented by <code>span</code> elements
      with this class.</dd>

      <dt id="class_CodeMirror_matchingbracket"><code>CodeMirror-matchingbracket</code>,
        <code>CodeMirror-matchingbracket</code></dt>
      <dd>These are used to style matched (or unmatched) brackets.</dd>
    </dl>

    <p>The actual lines, as well as the cursor, are represented
    by <code>pre</code> elements. By default no text styling (such as
    bold) that might change line height is applied. If you do want
    such effects, you'll have to give <code>CodeMirror pre</code> a
    fixed height. Also, you must still take care that character width
    is constant.</p>

    <p>If your page's style sheets do funky things to
    all <code>div</code> or <code>pre</code> elements (you probably
    shouldn't do that), you'll have to define rules to cancel these
    effects out again for elements under the <code>CodeMirror</code>
    class.</p>

    <h2 id="api">Programming API</h2>

    <p>A lot of CodeMirror features are only available through its API.
    This has the disadvantage that you need to do work to enable them,
    and the advantage that CodeMirror will fit seamlessly into your
    application.</p>

    <p>Whenever points in the document are represented, the API uses
    objects with <code>line</code> and <code>ch</code> properties.
    Both are zero-based. CodeMirror makes sure to 'clip' any positions
    passed by client code so that they fit inside the document, so you
    shouldn't worry too much about sanitizing your coordinates. If you
    give <code>ch</code> a value of <code>null</code>, or don't
    specify it, it will be replaced with the length of the specified
    line.</p>

    <dl>
      <dt id="getValue"><code>getValue() → string</code></dt>
      <dd>Get the current editor content.</dd>
      <dt id="setValue"><code>setValue(string)</code></dt>
      <dd>Set the editor content.</dd>

      <dt id="getSelection"><code>getSelection() → string</code></dt>
      <dd>Get the currently selected code.</dd>
      <dt id="replaceSelection"><code>replaceSelection(string)</code></dt>
      <dd>Replace the selection with the given string.</dd>

      <dt id="focus"><code>focus()</code></dt>
      <dd>Give the editor focus.</dd>

      <dt id="setOption"><code>setOption(option, value)</code></dt>
      <dd>Change the configuration of the editor. <code>option</code>
      should the name of an <a href="#config">option</a>,
      and <code>value</code> should be a valid value for that
      option.</dd>
      <dt id="getOption"><code>getOption(option) → value</code></dt>
      <dd>Retrieves the current value of the given option for this
      editor instance.</dd>

      <dt id="cursorCoords"><code>cursorCoords(start) → object</code></dt>
      <dd>Returns an <code>{x, y, yBot}</code> object containing the
      coordinates of the cursor relative to the top-left corner of the
      page. <code>yBot</code> is the coordinate of the bottom of the
      cursor. <code>start</code> is a boolean indicating whether you
      want the start or the end of the selection.</dd>
      <dt id="charCoords"><code>charCoords(pos) → object</code></dt>
      <dd>Like <code>cursorCoords</code>, but returns the position of
      an arbitrary characters. <code>pos</code> should be
      a <code>{line, ch}</code> object.</dd>
      <dt id="coordsChar"><code>coordsChar(object) → pos</code></dt>
      <dd>Given an <code>{x, y}</code> object (in page coordinates),
      returns the <code>{line, ch}</code> position that corresponds to
      it.</dd>

      <dt id="undo"><code>undo()</code></dt>
      <dd>Undo one edit (if any undo events are stored).</dd>
      <dt id="redo"><code>redo()</code></dt>
      <dd>Redo one undone edit.</dd>
      <dt id="historySize"><code>historySize() → object</code></dt>
      <dd>Returns an object with <code>{undo, redo}</code> properties,
      both of which hold integers, indicating the amount of stored
      undo and redo operations.</dd>

      <dt id="indentLine"><code>indentLine(line)</code></dt>
      <dd>Reset the given line's indentation to the indentation
      prescribed by the mode.</dd>

      <dt id="getSearchCursor"><code>getSearchCursor(query, start, caseFold) → cursor</code></dt>
      <dd>Used to implement search/replace
      functionality. <code>query</code> can be a regular expression or
      a string (only strings will match across lines—if they contain
      newlines). <code>start</code> provides the starting position of
      the search. It can be a <code>{line, ch}</code> object, or can
      be left off to default to the start of the
      document. <code>caseFold</code> is only relevant when matching a
      string. It will cause the search to be case-insensitive. A
      search cursor has the following methods:
        <dl>
          <dt><code>findNext(), findPrevious() → boolean</code></dt>
          <dd>Search forward or backward from the current position.
          The return value indicates whether a match was found. If
          matching a regular expression, the return value will be the
          array returned by the <code>match</code> method, in case you
          want to extract matched groups.</dd>
          <dt><code>from(), to() → object</code></dt>
          <dd>These are only valid when the last call
          to <code>findNext</code> or <code>findPrevious</code> did
          not return false. They will return <code>{line, ch}</code>
          objects pointing at the start and end of the match.</dd>
        </dl></dd>

      <dt id="getTokenAt"><code>getTokenAt(pos) → object</code></dt>
      <dd>Retrieves information about the token the current mode found
      at the given position (a <code>{line, ch}</code> object). The
      returned object has the following properties:
      <dl>
        <dt><code>start</code></dt><dd>The character (on the given line) at which the token starts.</dd>
        <dt><code>end</code></dt><dd>The character at which the token ends.</dd>
        <dt><code>string</code></dt><dd>The token's string.</dd>
        <dt><code>className</code></dt><dd>The class the mode assigned
        to the token. (Can be null when no class was assigned.)</dd>
      </dl></dd>

      <dt id="markText"><code>markText(from, to, className) → function</code></dt>
      <dd>Can be used to mark a range of text with a specific CSS
      class name. <code>from</code> and <code>to</code> should
      be <code>{line, ch}</code> objects. The method will return a
      function that can be called to remove the marking.</dd>

      <dt id="setMarker"><code>setMarker(line, text, className) → lineHandle</code></dt>
      <dd>Add a gutter marker for the given line. Gutter markers are
      shown in the line-number area (instead of the number for this
      line). Both <code>text</code> and <code>className</code> are
      optional. Setting <code>text</code> to a Unicode character like
      ● tends to give a nice effect. To put a picture in the gutter,
      set <code>text</code> to a space and <code>className</code> to
      something that sets a background image. If you
      specify <code>text</code>, the given text (which may contain
      HTML) will, by default, replace the line number for that line.
      If this is not what you want, you can include the
      string <code>%N%</code> in the text, which will be replaced by
      the line number.</dd>
      <dt id="clearMarker"><code>clearMarker(line)</code></dt>
      <dd>Clears a marker created
      with <code>setMarker</code>. <code>line</code> can be either a
      number or a handle returned by <code>setMarker</code> (since a
      number may now refer to a different line if something was added
      or deleted).</dd>
      <dt id="setLineClass"><code>setLineClass(line, className) → lineHandle</code></dt>
      <dd>Set a CSS class name for the given line. <code>line</code>
      can be a number or a line handle (as returned
      by <code>setMarker</code> or this function).
      Pass <code>null</code> to clear the class for a line.</dd>

      <dt id="lineInfo"><code>lineInfo(line) → object</code></dt>
      <dd>Returns the line number, text content, and marker status of
      the given line, which can be either a number or a handle
      returned by <code>setMarker</code>. The returned object has the
      structure <code>{line, text, markerText, markerClass}</code>.</dd>

      <dt id="addWidget"><code>addWidget(pos, node, scrollIntoView)</code></dt>
      <dd>Puts <code>node</code>, which should be an absolutely
      positioned DOM node, into the editor, positioned right below the
      given <code>{line, ch}</code> position.
      When <code>scrollIntoView</code> is true, the editor will ensure
      that the entire node is visible (if possible). To remove the
      widget again, simply use DOM methods (move it somewhere else, or
      call <code>removeChild</code> on its parent).</dd>

      <dt id="matchBrackets"><code>matchBrackets()</code></dt>
      <dd>Force matching-bracket-highlighting to happen.</dd>

      <dt id="lineCount"><code>lineCount() → number</code></dt>
      <dd>Get the number of lines in the editor.</dd>

      <dt id="getCursor"><code>getCursor(start) → object</code></dt>
      <dd><code>start</code> is a boolean indicating whether the start
      or the end of the selection must be retrieved. If it is not
      given, the current cursor pos, i.e. the side of the selection
      that would move if you pressed an arrow key, is chosen.
      A <code>{line, ch}</code> object will be returned.</dd>
      <dt id="somethingSelected"><code>somethingSelected() → boolean</code></dt>
      <dd>Return true if any text is selected.</dd>
      <dt id="setCursor"><code>setCursor(pos)</code></dt>
      <dd>Set the cursor position. You can either pass a
      single <code>{line, ch}</code> object, or the line and the
      character as two separate parameters.</dd>
      <dt id="setSelection"><code>setSelection(start, end)</code></dt>
      <dd>Set the selection range. <code>start</code>
      and <code>end</code> should be <code>{line, ch}</code> objects.</dd>

      <dt id="getLine"><code>getLine(n) → string</code></dt>
      <dd>Get the content of line <code>n</code>.</dd>
      <dt id="setLine"><code>setLine(n, text)</code></dt>
      <dd>Set the content of line <code>n</code>.</dd>
      <dt id="removeLine"><code>removeLine(n)</code></dt>
      <dd>Remove the given line from the document.</dd>

      <dt id="getRange"><code>getRange(from, to) → string</code></td>
      <dd>Get the text between the given points in the editor, which
      should be <code>{line, ch}</code> objects.</dd>
      <dt id="replaceRange"><code>replaceRange(string, from, to)</code></dt>
      <dd>Replace the part of the document between <code>from</code>
      and <code>to</code> with the given string. <code>from</code>
      and <code>to</code> must be <code>{line, ch}</code>
      objects. <code>to</code> can be left off to simply insert the
      string at position <code>from</code>.</dd>
    </dl>

    <p>The following are more low-level methods:</p>

    <dl>
      <dt id="operation"><code>operation(func) → result</code></dt>
      <dd>CodeMirror internally buffers changes and only updates its
      DOM structure after it has finished performing some operation.
      If you need to perform a lot of operations on a CodeMirror
      instance, you can call this method with a function argument. It
      will call the function, buffering up all changes, and only doing
      the expensive update after the function returns. This can be a
      lot faster. The return value from this method will be the return
      value of your function.</dd>

      <dt id="refresh"><code>refresh()</code></dt>
      <dd>If your code does something to change the size of the editor
      element (window resizes are already listened for), or unhides
      it, you should probably follow up by calling this method to
      ensure CodeMirror is still looking as intended.</dd>

      <dt id="getInputField"><code>getInputField() → textarea</code></dt>
      <dd>Returns the hiden textarea used to read input.</dd>
      <dt id="getWrapperElement"><code>getWrapperElement() → node</code></dt>
      <dd>Returns the DOM node that represents the editor. Remove this
      from your tree to delete an editor instance.</dd>
    </dl>

    <p id="fromTextArea">Finally, the <code>CodeMirror</code> object
    itself has a method <code>fromTextArea</code>. This takes a
    textarea DOM node as first argument and an optional configuration
    object as second. It will replace the textarea with a CodeMirror
    instance, and wire up the form of that textarea (if any) to make
    sure the editor contents are put into the textarea when the form
    is submitted. A CodeMirror instance created this way has two
    additional methods:</p>

    <dl>
      <dt id="save"><code>save()</code></dt>
      <dd>Copy the content of the editor into the textarea.</dd>

      <dt id="toTextArea"><code>toTextArea()</code></dt>
      <dd>Remove the editor, and restore the original textarea (with
      the editor's current content).</dd>
    </dl>

    <h2 id="modeapi">Writing CodeMirror Modes</h2>

    <p>Modes typically consist of a JavaScript file and a CSS file.
    The CSS file (see, for
    example <a href="mode/javascript/javascript.css"><code>javascript.css</code></a>)
    defines the classes that will be used to style the syntactic
    elements of the code, and the script contains the logic to
    actually assign these classes to the right pieces of text.</p>

    <p>You'll usually want to use some kind of prefix for your CSS
    classes, so that they are unlikely to clash with other classes,
    both those used by other modes and those defined by the page in
    which CodeMirror is embedded.</p>

    <p id="defineMode">The mode script should
    call <code>CodeMirror.defineMode</code> to register itself with
    CodeMirror. This function takes two arguments. The first should be
    the name of the mode, for which you should use a lowercase string,
    preferably one that is also the name of the files that define the
    mode (i.e. <code>"xml"</code> is defined <code>xml.js</code>). The
    second argument should be a function that, given a CodeMirror
    configuration object (the thing passed to
    the <code>CodeMirror</code> function) and a mode configuration
    object (as in the <a href="#option_mode"><code>mode</code></a>
    option), returns a mode object.</p>

    <p>Typically, you should use this second argument
    to <code>defineMode</code> as your module scope function (modes
    should not leak anything into the global scope!), i.e. write your
    whole mode inside this function.</p>

    <p>The main responsibility of a mode script is <em>parsing</em>
    the content of the editor. Depending on the language and the
    amount of functionality desired, this can be done in really easy
    or extremely complicated ways. Some parsers can be stateless,
    meaning that they look at one element (<em>token</em>) of the code
    at a time, with no memory of what came before. Most, however, will
    need to remember something. This is done by using a <em>state
    object</em>, which is an object that can be mutated every time a
    new token is read.</p>

    <p id="startState">Modes that use a state must define
    a <code>startState</code> method on their mode object. This is a
    function of no arguments that produces a state object to be used
    at the start of a document.</p>

    <p id="token">The most important part of a mode object is
    its <code>token(stream, state)</code> method. All modes must
    define this method. It should read one token from the stream it is
    given as an argument, optionally update its state, and return a
    CSS class string, or <code>null</code> for tokens that do not have
    to be styled.<p>

    <p id="StringStream">The stream object encapsulates a line of code
    (tokens may never span lines) and our current position in that
    line. It has the following API:</p>

    <dl>
      <dt><code>eol() → boolean</code></dt>
      <dd>Returns true only if the stream is at the end of the
      line.</dd>
      <dt><code>sol() → boolean</code></dt>
      <dd>Returns true only if the stream is at the start of the
      line.</dd>

      <dt><code>peek() → character</code></dt>
      <dd>Returns the next character in the stream without advancing
      it. Will return <code>undefined</code> at the end of the
      line.</dd>
      <dt><code>next() → character</code></dt>
      <dd>Returns the next character in the stream and advances it.
      Also returns <code>undefined</code> when no more characters are
      available.</dd>

      <dt><code>eat(match) → character</code></dt>
      <dd><code>match</code> can be a character, a regular expression,
      or a function that takes a character and returns a boolean. If
      the next character in the stream 'matches' the given argument,
      it is consumed and returned. Otherwise, <code>undefined</code>
      is returned.</dd>
      <dt><code>eatWhile(match) → boolean</code></dt>
      <dd>Repeatedly calls <code>eat</code> with the given argument,
      until it fails. Returns true if any characters were eaten.</dd>
      <dt><code>eatSpace() → boolean</code></dt>
      <dd>Shortcut for <code>eatWhile</code> when matching
      white-space.</dd>
      <dt><code>skipToEnd()</code></dt>
      <dd>Moves the position to the end of the line.</dd>
      <dt><code>skipTo(ch) → boolean</code></dt>
      <dd>Skips to the next occurrence of the given character, if
      found. Returns true if the character was found.</dd>
      <dt><code>match(pattern, consume, caseFold) → boolean</code></dt>
      <dd>Act like a
      multi-character <code>eat</code>—if <code>consume</code> is true
      or not given—or a look-ahead that doesn't update the stream
      position—if it is false. <code>pattern</code> can be either a
      string or a regular expression starting with <code>^</code>.
      When it is a string, <code>caseFold</code> can be set to true to
      make the match case-insensitive. When successfully matching a
      regular expression, the returned value will be the array
      returned by <code>match</code>, in case you need to extract
      matched groups.</dd>

      <dt><code>backUp(n)</code></dt>
      <dd>Backs up the stream <code>n</code> characters. Backing it up
      further than the start of the current token will cause things to
      break, so be careful.</dd>
      <dt><code>column() → integer</code></dt>
      <dd>Returns the column (taking into account tabs) at which the
      current token starts. Can be used to find out whether a token
      starts a new line.</dd>
      <dt><code>indentation() → integer</code></dt>
      <dd>Tells you how far the current line has been indented, in
      spaces. Corrects for tab characters.</dd>

      <dt><code>current() → string</code></dt>
      <dd>Get the string between the start of the current token and
      the current stream position.</dd>
    </dl>

    <p id="copyState">Because state object are mutated, and CodeMirror
    needs to keep valid versions of a state around so that it can
    restart a parse at any line, copies must be made of state objects.
    The default algorithm used is that a new state object is created,
    which gets all the properties of the old object. Any properties
    which hold arrays get a copy of these arrays (since arrays tend to
    be used as mutable stacks). When this is not correct, for example
    because a mode mutates non-array properties of its state object, a
    mode object should define a <code>copyState</code> method,
    which is given a state and should return a safe copy of that
    state.</p>

    <p id="indent">If you want your mode to provide smart indentation
    (see <a href="#option_enterMode"><code>entermode</code></a>
    and <a href="#option_tabMode"><code>tabMode</code></a> when they
    have a value of <code>"indent"</code>), you must define
    an <code>indent(state, textAfter)</code> method on your mode
    object.</p>

    <p>The indentation method should inspect the given state object,
    and optionally the <code>textAfter</code> string, which contains
    the text on the line that is being indented, and return an
    integer, the amount of spaces to indent. It should usually take
    the <a href="#option_indentUnit"><code>indentUnit</code></a>
    option into account.</p>

    <p id="electricChars">Finally, a mode may define
    an <code>electricChars</code> property, which should hold a string
    containing all the characters that should trigger the behaviour
    described for
    the <a href="#option_electricChars"><code>electricChars</code></a>
    option.</p>

    <p>So, to summarize, a mode <em>must</em> provide
    a <code>token</code> method, and it <em>may</em>
    provide <code>startState</code>, <code>copyState</code>,
    and <code>indent</code> methods. For an example of a trivial mode,
    see the <a href="mode/diff/diff.js">diff mode</a>, for a more
    involved example, see
    the <a href="mode/javascript/javascript.js">JavaScript
    mode</a>.</p>

    <p>Sometimes, it is useful for modes to <em>nest</em>—to have one
    mode delegate work to another mode. An example of this kind of
    mode is the <a href="mode/htmlmixed/htmlmixed.js">mixed-mode HTML
    mode</a>. To implement such nesting, it is usually necessary to
    create mode objects and copy states yourself. To create a mode
    object, there are <code>CodeMirror.getMode(options,
    parserConfig)</code>, where the first argument is a configuration
    object as passed to the mode constructor function, and the second
    argument is a mode specification as in
    the <a href="#option_mode"><code>mode</code></a> option. To copy a
    state object, call <code>CodeMirror.copyState(mode, state)</code>,
    where <code>mode</code> is the mode that created the given
    state.</p>

    <p>To make indentation work properly in a nested parser, it is
    advisable to give the <code>startState</code> method of modes that
    are intended to be nested an optional argument that provides the
    base indentation for the block of code. The JavaScript and CSS
    parser do this, for example, to allow JavaScript and CSS code
    inside the mixed-mode HTML mode to be properly indented.</p>

    <p>Finally, it is possible to associate your mode, or a certain
    configuration of your mode, with
    a <a href="http://en.wikipedia.org/wiki/MIME">MIME</a> type. For
    example, the JavaScript mode associates itself
    with <code>text/javascript</code>, and its JSON variant
    with <code>application/json</code>. To do this,
    call <code>CodeMirror.defineMIME(mime, modeSpec)</code>,
    where <code>modeSpec</code> can be a string or object specifying a
    mode, as in the <a href="#option_mode"><code>mode</code></a>
    option.</p>

</div><div class="rightsmall blk">

    <h2>Contents</h2>

    <ul>
      <li><a href="#overview">Overview</a></li>
      <li><a href="#usage">Basic Usage</a></li>
      <li><a href="#config">Configuration</a></li>
      <li><a href="#styling">Customized Styling</a></li>
      <li><a href="#api">Programming API</a></li>
      <li><a href="#modeapi">Writing CodeMirror Modes</a></li>
    </ul>

</div></div>

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